Current steering digital-to-analog converter

Abstract

A current steering digital-to-analog converter (DAC) is provided. At least two lower-resolution DACs are used for converting a high-resolution digital signal. One of the two lower-resolution DACs is used for converting the most significant bits (MSB) of the high-resolution digital signal. The other of the two lower-resolution DACs is used for converting the least significant bits (LSB) of the high-resolution digital signal. By such arrangement, a device mismatch problem is avoided and the chance of variation occurrence during manufacturing process is reduced. The arrangement also simplifies the layout in the significantly scaled-down chip area.

1. A current steering digital-to-analog converter (DAC), used for converting a digital signal having a first bit number, the current steering DAC comprising:
 a first DAC, used for converting a digital signal having a second bit number and outputting a first output current; 
 a second DAC, used for converting a digital signal having a third bit number and outputting a second output current, wherein the sum of the second bit number and the third bit number is equal to the first bit number; 
 a first current mirror, used for mapping and outputting the first output current of the first DAC as a first mapped output current, wherein the first mapped output current is a magnified output current by multiplying the first output current of the first DAC by 2 N , wherein N is an integer, and N=first bit number−second bit number; and 
 a second current mirror, used for mapping and outputting the second output current of the second DAC as a second mapped output current, wherein the output of the current steering DAC is the total current of the first mapped output current and the second mapped output current. 
 
   
   
     2. The current steering DAC as claimed in  claim 1 , wherein the first mapped output current mapped and output by the first current mirror is less than the first output current of the first DAC. 
   
   
     3. The current steering DAC as claimed in  claim 1 , wherein the ratio between the first output current output by the first DAC and the first mapped output current mapped and output by the first current mirror can be adjusted according to the first output current. 
   
   
     4. The current steering DAC as claimed in  claim 1 , wherein the second bit number is the most significant bits (MSB) of the first bit number, and the third bit number is the least significant bits (LSB) of the first bit number. 
   
   
     5. The current steering DAC as claimed in  claim 1 , further comprising a bias generation unit used for providing a constant bias to the first DAC and the second DAC, so that the digital-to-analog conversion can be performed accordingly. 
   
   
     6. The current steering DAC as claimed in  claim 1 , further comprising a first bias generation unit used for providing a first constant bias to the first DAC and a second bias generation unit used for providing a second constant bias to the second DAC, so that the digital-to-analog conversion can be performed accordingly. 
   
   
     7. The current steering DAC as claimed in  claim 1 , wherein the first DAC includes a plurality of control units, selectively turned on according to a received digital signal having the second bit number, and a first input current is converted into the first output current of the first DAC accordingly. 
   
   
     8. The current steering DAC as claimed in  claim 7 , wherein the received digital signal having the second bit number is received by a control device and used for controlling the control units accordingly. 
   
   
     9. The current steering DAC as claimed in  claim 1 , wherein the second DAC includes a plurality of control units, selectively turned on according to a received digital signal having the third bit number, and a second input current is converted into the second output current of the second DAC accordingly. 
   
   
     10. The current steering DAC as claimed in  claim 9 , wherein the received digital signal having the third bit number is received by a control device and used for controlling the control units accordingly. 
   
   
     11. A current steering DAC, used for converting a (M+N)-bit digital signal, wherein M and N are integers, the current steering DAC comprising:
 a first DAC, used for converting an M-bit digital signal and outputting a first output current; 
 a second DAC, used for converting a N-bit digital signal and outputting a second output current; and 
 a current mirror, used for mapping and outputting the first output current of the first DAC as a mapped output current, wherein the mapped output current is a magnified output current by multiplying the first output current of the first DAC by 2 N , and the output of the current steering DAC is the total current of the mapped output current of the current mirror and the second output current of the second DAC. 
 
   
   
     12. The current steering DAC as claimed in  claim 11 , wherein the M-bit digital signal received and converted by the first DAC is the MSB of the (M+N)-bit digital signal, and the N-bit digital signal received and converted by the second DAC is the LSB of the (M+N)-bit digital signal. 
   
   
     13. The current steering DAC as claimed in  claim 11 , wherein the first DAC includes a plurality of control units, selectively turned on according to the received M-bit digital signal, and a first input current is converted into the first output current of the first DAC accordingly. 
   
   
     14. The current steering DAC as claimed in  claim 13 , wherein the M-bit digital signal received by the first DAC is received by a control device and is used for controlling the control units accordingly. 
   
   
     15. The current steering DAC as claimed in  claim 11 , the second DAC includes a plurality of control units, selectively turned on according to the received N-bit digital signal, and a second input current is converted into the second output current of the second DAC accordingly. 
   
   
     16. The current steering DAC as claimed in  claim 15 , wherein the N-bit digital signal received by the second DAC is received by a control device and is used for controlling the control units accordingly. 
   
   
     17. A current steering DAC, used for converting a (M+N)-bit digital signal, wherein M and N are integers, the current steering DAC comprising:
 a first DAC, used for converting the M-bit digital signal and outputting a first output current; 
 a second DAC, used for converting the N-bit digital signal and outputting a second output current; and 
 a first current mirror, used for mapping and outputting the first output current of the first DAC as a first mapped output current, wherein the first mapped output current is the product of the first output current and 2 (N−X) , wherein X is an integer greater than or equal to 0, and the second mapped output current is the product of the second output current and 2 −X ; 
 a second current mirror, used for mapping and outputting the second output current of the second DAC as a second mapped output current, wherein the output of the current steering DAC is the total current of the first mapped output current and the second mapped output current.